Infrared and DFT investigations of the XC[triple bond]ReX3 and HC[triple bond]ReX3 complexes: Jahn-Teller distortion and the methylidyne C-X(H) stretching absorptions

The XC[triple bond]ReX3 complexes (X = F, Cl) are produced by CX(4) reaction with laser-ablated Re atoms, following oxidative C-X insertion and alpha-halogen migration in favor of the carbon-metal triple bond and are identified through the observation of characteristic absorptions in the argon matrix infrared spectra and comparison with vibrational frequencies calculated by density functional theory. The methylidyne C-F and C-Cl stretching absorptions are observed near 1584 and 1328 cm-1, and the C-H stretching modes for HC[triple bond]ReX3 at 3104 and 3097 cm(-1), respectively, which are substantially higher than the precursor stretching modes and in agreement with the general trend that higher s-orbital character in carbon hybridization leads to a higher stretching frequency. The Jahn-Teller effect in the doublet-state XC[triple bond]ReX3 and HC[triple bond]ReX3 complexes gives rise to distorted structures with Cs symmetry and two equivalent longer Re-X bonds and one slightly shorter Re-X bond.     

P2 addition to terminal phosphide M[triple bond]P triple bonds: a rational synthesis of cyclo-P3 complexes

The diphosphaazide complex (Mes*NPP)Nb(N[Np]Ar)3 (Mes* = 2,4,6-tri-tert-butylphenyl, Np = neopentyl, Ar = 3,5-Me2C6H3), 1, has previously been reported to lose the P2 unit upon gentle heating, to form (Mes*N)Nb(N[Np]Ar)3, 2. The first-order activation parameters for this process have been estimated here using an Eyring analysis to have the values Delta H(double dagger) = 19.6(2) kcal/mol and Delta S(double dagger) = -14.2(5) eu. The eliminated P2 unit can be transferred to the terminal phosphide complexes P[triple bond]M(N[(i)Pr]Ar)3, 3-M (M = Mo, W), and [P[triple bond]Nb(N[Np]Ar)3](-), 3-Nb, to give the cyclo-P3 complexes (P3)M(N[(i)Pr]Ar)3 and [(P3)Nb(N[Np]Ar)3](-). These reactions represent the formal addition of a P[triple bond]P triple bond across a M[triple bond]P triple bond and are the first efficient transfers of the P2 unit to substrates present in stoichiometric quantities. The related complex (OC)5W(Mes*NPP)Nb(N[Np]Ar)3, 1-W(CO)5, was used to transfer the (P2)W(CO)5 unit in an analogous manner to the substrates 3-M (M = Mo, W, Nb) as well as to [(OC)5WP[triple bond]Nb(N[Np]Ar)3](-). The rate constants for the fragmentation of 1 and 1-W(CO)5 were unchanged in the presence of the terminal phosphide 3-Mo, supporting the hypothesis that molecular P2 and (P2)W(CO)5, respectively, are reactive intermediates. In a reaction related to the combination of P[triple bond]P and M[triple bond]P triple bonds, the phosphaalkyne AdC[triple bond]P (Ad = 1-adamantyl) was observed to react with 3-Mo to generate the cyclo-CP2 complex (AdCP2)Mo(N[(i)Pr]Ar)3. Reactions of the electrophiles Ph3SnCl, Mes*NPCl, and AdC(O)Cl with the anionic, nucleophilic complexes [(OC)5W(P3)Nb(N[Np]Ar)3](-) and [{(OC)5W}2(P3)Nb(N[Np]Ar)3](-) yielded coordinated eta(2)-triphosphirene ligands. The Mes*NPW(CO)5 group of one such product engages in a fluxional ring-migration process, according to NMR spectroscopic data. The structures of (OC)5W(P3)W(N[(i)Pr]Ar)3, [(Et2O)Na][{(OC)5W}2(P3)Nb(N[Np]Ar)3], (AdCP2)Mo(N[(i)Pr]Ar)3, (OC)5W(Ph3SnP3)Nb(N[Np]Ar)3, Mes*NP(W(CO)5)P3Nb(N[Np]Ar)3, and {(OC)5W}2AdC(O)P3Nb(N[Np]Ar)3, as determined by X-ray crystallography, are discussed in detail.     

Twofold hydrogallation of C triple bonds c triple bonds by H-GaCl(2)-synthesis of chelating Lewis acids and their application in adduct formation

The twofold addition of Ga-H to Ctriple bonds C triple bonds (hydrogallation) did not succeed by treatment of alkynes with an excess of dialkylgallium hydrides. In contrast, double hydrogallation was easily achieved by the reactions of H-GaCl(2) with trimethylsilyl-substituted alkynes [trimethylsilylphenylethyne and 1,4-bis(trimethylsilylethynyl)benzene] in appropriate stoichiometric ratios. The monoalkyne yielded the compound [H(5)C(6)-CH(2)-C(SiMe(3))(GaCl(2))(2)](2), 1, which was only sparingly soluble in n-hexane. Crystal structure determination revealed a dimeric formula unit possessing two parallel Ga(2)Cl(2) heterocycles in the solid state. Treatment of the dialkyne with four equivalents of the hydride gave a colorless precipitate, which was completely insoluble in hydrocarbons. Addition of diethyl ether to both products afforded soluble and monomeric etherates 1(OEt(2))(2) and 2 in which the two or four gallium atoms, respectively, were coordinated by ether molecules. Preliminary experiments with simple Lewis bases showed the principle capability of 1 to act as an effective chelating Lewis acid. Adducts of the type [H(5)C(6)-CH(2)-C(SiMe(3))(GaCl(2))(GaClX)(micro-Cl)]- (4-6) resulted upon treatment with halide ions (X = Cl, Br, I).     

Stable nitroxyl radicals with triple bonds: 4-acetylenyl-3-imidazoline-3-oxide-1-oxyls

Cross-coupling reaction of 1-hydroxy-2,2,5,5-tetramethyl-4-[2-(p-iodophenyl)vinyl]-3-imidazoline-3-oxide with copper(I) salts of 1-aryl(hetaryl)alkynes leads to the corresponding 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)vinyl]-3-imidazoline-3-oxide-1-oxyls in high yields.     

Intramolecular cycloaddition of N-phthalimidoaziridines to double and triple carbon-carbon bonds

Thermolysis of 3-(2-allyloxyphenyl)- or 3-(2-propargyloxyphenyl)-1-phthalimidoaziridine-2-carboxylic acid derivatives results in stereospecific intramolecular cycloaddition of intermediate N-phthalimidoazomethine ylides to double or triple carbon-carbon bonds. This leads to condensed N-phthalimidopyrrolidines, N-phthalimidopyrrolines, or products of their subsequent transformations. On the other hand, thermolysis of similar dimethyl 3-aryl-1-phthalimidoaziridine-2,2-dicarboxylates gives exclusively 5-methoxyoxazoles, the products of a competitive 1,5-dipolar electrocyclization.     

Two types of rhodium-catalyzed CS/CS metathesis reactions: formation of CS/CS bonds and CC/SS bonds

A rhodium complex catalyzes two types of single bond metathesis reactions of two CS bonds depending on the added ligand: CS/CS to CS/CS metathesis and CS/CS to CC/SS metathesis. In the presence of a catalytic amount of RhH(PPh₃)₄ and 1,1′-bis(diphenylphosphino)ferrocene (dppf), two 1-alkylthioalkynes exchange alkylthio groups to give equilibrium mixtures of four 1-alkylthioalkynes. When tris(p-methoxyphenyl)phosphine or diphenylmethylphosphine is used, 1,3-butadiynes are obtained.     

Construction of 3-allylidene-4-vinyltetrahydrofurans and 3-allylidene-4-vinylpyrrolidines via sequential domino allylation/olefination of C-C triple bonds

An efficient method via sequential domino allylation/olefination of C-C triple bonds for the syntheses of five-membered heterocycles was developed by treatment 1,6-enynes with alkenes in the presence of a palladium catalyst. The configurations of the 1,3-dienes of the five-membered heterocycles are stereocontrolled.     

Heterolytic addition of E-H bonds across Pt-P bonds in Pt N-heterocyclic phosphenium/phosphido complexes

The reactivity of E-H bonds (E = S, O, Cl) with Pt(II) complexes ligated by an N-heterocyclic phosphido-containing diphosphine ligand have been investigated. Addition of PhSH to [(PPP)Pt(PPh(3))][PF(6)] (1) results in clean formation of [(PP(H)P)Pt(SPh)][PF(6)] (3), in which the substrate has added across the Pt-P(NHP) bond. Similar reactivity occurs when 1 is treated with ROH (R = Ph, Me), but in this case the O-H bond adds across the Pt-P bond in the opposite direction producing [(PP(OR)P)Pt(H)(PPh(3))][PF(6)] (R = Ph (4), Me (5)). HCl addition to 1 cleanly generates [(PP(H)P)PtCl][PF(6)] (6(PF6)). The neutral Pt-NHP complex (PPP)PtCl (2) exhibits similar reactivity; however, in the presence of the nucleophilic Cl(-) anion, the (PP(OR)P)Pt(H)Cl species presumably generated via addition of ROH (R = Me, Et) undergoes an Arbuzov-like dealkylation reaction to exclusively form the N-heterocylic phosphinito species (PP(O)P)Pt(H) (7).     

Intramolecular hydrogen bonds in complexones and their role in the formation of complexes with metals

Data on the shift of the¹H,¹³C, and¹⁵N signals during the protonation of complexones are analyzed with due regard to all the principal contributions to the chemical shift. Data are obtained on the structure of the mono- and diprotonated forms of the complexones in aqueous solutions, and the structure of the complexones in the crystals and solutions is compared. It is shown that the proton assembles all the donating groups of the complexone into a single coordination unit and creates a matrix, in which the metal complex is formed.Institute of General and Inorganic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 3, pp. 323–329, May–June, 1991. Original article submitted February 15, 1991.     

Therbiological character of fatty acids with triple bonds. 3. The metabolism of tariric acid

Octadec-6-ynoic acid (tariric acid) fed to rats as triglyceride is incorporated both into depot fat and liver lipids. As a metabolite the so far undesdribed dec-4-ene-6-ynedioic acid, HOOC? (CH₂)₂? CH?CH? CGC? (CH₂)₂? COOH, was isolated from the urine.     

Electron pairing and chemical bonds: Chemical bonds from the condition of minimum fluctuation of electron pair

The role of electron pairing in chemical bonding stressed by the Lewis electron-pair model of the chemical bond is analyzed and discussed from the point of view of the proposal that chemical bonds are the regions of space populated roughly by two electrons and which at the same time exhibit low fluctuation of an electron pair. Based on this assumption, we have been able to introduce a new localization procedure, the output of which are just the orbitals (chemical bonds) satisfying the criterion of minimum pair fluctuation. It has been shown that these orbitals remarkably well display the most important attributes of chemical bonds, namely, the localization in the regions where classical bonds are expected and there is very high transferability from one molecule to another. The applicability of this procedure as a new means of the analysis and the visualization of the molecular structure is also discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 193–200, 1998     

Hydrogen bonds and ionic interactions in Guanidine/Guanidinium complexes: a computational case study

It is frequently said that hydrogen bonds (HBs) are enhanced by ionic interactions and in this article we intend to determine the degree at which this reinforcement happens. Considering our interest in the Guanidine(neutral)/Guanidinium(cation) system and its particular nature, all the possible 1:1 complexes with the Chloride(anion)/Hydrochloric acid(neutral) system have been studied at different levels of computation (B3LYP with 6-31+G* and TZVP basis sets; MP2 with 6-31+G*, 6-311++G** and aug-cc-pVDZ basis sets; CBS-QB3 and G3MP2). The nature of these interactions established in all the systems and, when possible, at all the levels of computation used in this study, has been analyzed using Atoms in Molecules and Natural Bond Orbital methodologies. By examining the interaction energy, the electron density at the bond critical bonds, the atomic energy, the charge transfer, the orbital energy, and the deformation energy we can conclude that HBs are stronger when the ionic interaction is stronger. Thus, both interactions do not work in an independent manner but one reinforces the other to different degrees depending on the nature of the charges present. Several correlations with the interaction energy have been found and a partition of the contributions of both the HB and ionic forces to the total interactions is proposed.     

Effect of Ligand X in Cp*TiX3/MAO Catalysts on the Polymerization of Vinyl Chloride

The polymerization of vinyl chloride with Cp*TiX₃/MAO (X = OCH₃, OC₄H₉, OPh, Cl) catalysts in CH₂Cl₂ was investigated. The activity of the Cp*TiX₃/MAO catalytic systems depends on ligand X in that increased activity was found for increasing electron‐donating capacity of X. The relationship between Hammet's σ_m of ligand X and polymer yield gave a straight line, indicating that the electronic effect of X plays an important role.     

Preferential formation of the different hydrogen bonds and their effects in tetrahydrofuran and tetrahydropyran microhydrated complexes

The role of cycloether-water (c-w) and water-water (w-w) hydrogen bonds (H-bonds) on the stability of the tetrahydrofuran THF/(H(2)O)(n) and the tetrahydropyran THP/(H(2)O)(n) complexes with n = 1-4 was investigated herein using the density functional and ab initio methods and the atoms in molecules theory. Geometry optimizations for these complexes were carried out with various possible initial guess structures. It was revealed that the major contributions of the mono and dihydrated complexes came from c-w H-bonds. A competition between c-w and w-w H-bonds contribution was observed for trihydrated complexes. For most of tetrahydrated complexes, the inter-water H-bonds provided the greatest contribution, whereas the c-w contributions were small but not negligible. It was confirmed that to produce a hydrophobic hydration of cycloethers, the C-H···O(w) H-bond should be associated with a network of H-bonds that connects both portions of the solute, through the formation of a bifunctional H-bond. A linear correlation is obtained for the sum of electron density at the bond critical points (ρ(b)) with the interaction energy (ΔE) and with the solute-solvent interaction energy (ΔE(s-w)) of the microhydrated complexes. In addition, a new way to estimate the energetic contribution as well as the preferential formation of the different H-bonds based completely on ρ(b) was found. Even more, it allows to differentiate the contribution from c-w interactions in both hydrophilic and hydrophobic contributions, it is therefore a useful tool for studying the hydration of large biomolecules. The analysis of the modifications in the atomic and group properties brought about by successive addition of H(2)O molecules allowed to pinpoint the atoms or molecular groups that undergo the greatest changes in electron population and energetic stabilization. It was identified that the remarkable stabilization of the water oxygen atoms is crucial for the stabilization of the complexes.     

The catalysis of the electrochemical reduction of alkyl bromides by nickel complexes: The formation of carboncarbon bonds

The square planar, macrocyclic nickel complex, N, N′-ethylenebis(salicylideneiminato)nickel(II), is shown to be an effective catalyst for the electrochemical reduction of substituted alkyl bromides; this indirect cathodic reduction can lead to a good yield of dimeric products. The reduction of alkyl bromides in the presence of an activated olefin is shown to lead to mixtures of products compatible with radical addition to the double bond. The mechanism of the reaction of nickel(I) complexes with alkyl bromides is discussed in the light of these results.     

First diastereoselective formation of lanthanide triple helical complexes with a terdentate chiral C2 symmetric ligand

Steric interactions between three enantiopure terdentate ligands leads to the diastereoselective formation of luminescent triple helical lanthanide complexes.     

Selective synthesis of fluorinated furan derivatives via AgNO3-catalyzed activation of an electronically deficient triple bond

The transition metal-catalyzed direct activation of electron deficient triple bonds was investigated by using the combined electron withdrawing effects of two fluorine atoms to modulate the electronic density of the triple bond. With use of catalytic amounts of AgNO3 (10 mol %) the synthesis of substituted 3,3-difluoro-4,5-dihydrofurans from gem-difluorohomopropargyl alcohols occurred in excellent NMR yields. Treatment of these dihydrofurans with SiO2 or Pd/H2 yielded the corresponding 3-fluorinated furans and 3,3-difluorotetrahydrofurans.